Concept:Tracing family relationships step-by-step from given statements.
Explanation:A is sister of B, so A is female and they share parents.
B is brother of C, so B and C are siblings; C is male (son of D).
Thus A, B, C are all siblings.
C is son of D, so D is a parent of C.
Since A is sibling of C, D is also a parent of A.
Therefore, D can be mother or father, but only "Mother" is among the options.
Answer:Mother